Thai police say an Iranian man bought the airfares for two men who boarded a missing plane with stolen passports.

Three days after the Malaysia Airlines flight carrying 239 people vanished between Kuala Lumpur and Beijing, a search operation involving several countries has found no sign of the aircraft.

The airline has said search and rescue teams are expanding the scope of their search beyond the plane's flight path to western Malaysia at the Straits of Malacca.

A Vietnamese rescue crew return from a search

Authorities are trying to find out more about the two mystery passengers who had one-way tickets to Europe and were travelling on Austrian and Italian passports stolen in Thailand in the past two years.

He added: "Do you know a footballer by the name of (Mario) Balotelli? (This is) what he looks like. I don't want to dwell on this but the men are not Asian-looking."

Thai Police Lt Col Ratchthapong Tia-sood has revealed that a travel agency in the beach resort of Pattaya, Grand Horizon, sold the tickets for the two men to an Iranian man known only as Mr Ali.

"We have to look further into this Mr Ali's identity because it's almost a tradition to use an alias when doing business around here," he said.

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Grand Horizon's owner, Benjaporn Krutnait, told The Financial Times she believed Mr Ali was not linked to terrorism as he asked for cheapest tickets to Europe.

She also said Mr Ali - who had been regularly buying tickets from her for around three years - had not specified the Kuala Lumpur to Beijing flight.

Sky's Foreign Affairs Editor Sam Kiley said: "This is not an indication at all of any kind of Iranian government involvement.

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"There is a massive industry in Malaysia and Thailand of people traffickers smuggling people from place to place on stolen passports. It has to be seen in that context at this stage."

It is not known whether the two men had anything to do with the plane's disappearance, but security services are investigating whether the Boeing 777-200 was hijacked or destroyed in a terror attack.

Malaysian Transport Minister Hishammuddin Hussein said biometric information and CCTV footage of the men has been shared with Chinese and US intelligence agencies, which were helping with the investigation.

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Officials are discussing whether images of the men should be made public as part of an appeal for information, while Interpol said additional "suspect" documents are under review.

Authorities admit they are "puzzled" by the "unprecedented" disappearance of the plane.

The search effort, involving at least 34 aircraft and 40 ships from 10 countries, has widened to a 100-nautical mile (115-mile, 185-km) radius.

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Earlier reports of debris spotted in the South China Sea, including an aircraft door, have not been confirmed, while a possible sighting of a section of the plane's tail has been ruled out.

Rescuers are also responding to reports of debris floating in the sea south of Hong Kong.

It has also been confirmed that samples of oil taken from a slick in the South China Sea came from a ship, not the missing aircraft.

Video:Relatives' Fears Over Missing Plane

With no confirmation that the Boeing 777 has crashed, hundreds of distraught relatives are still waiting anxiously for any news.

Nearly two-thirds of the passengers on the flight were Chinese and if the loss of the plane is confirmed, it would be the country's second-worst air disaster.